The proposal aims to identify the neural substrates in the primate brain that are responsible for abnormal socio-emotional behavior. This understanding is vital for developing both diagnostic and therapeutic approaches to identify and treat the abnormal brain circuitry in neuropsychiatric conditions such as affective and anxiety disorders. The field of social behavior research still lacks appropriate animal models for social pathology that leads to inappropriate aggression, social anxiety/phobias, social withdrawal/detachment, impulsivity, or defensiveness. The study of the neurobiology of social behavior in the nonhuman primate is especially promising since the impairment in social interactions and emotional processing generates symptomatology that resembles psychopathology observed in human patients. The proposed research seeks to investigate the novel components of the amygdala-based network that regulate socioemotional responses in nonhuman primates in order to account for imbalances that can give rise to psychopathology in the absence of structural lesions. We have determined that reversible pharmacological manipulations of specific sites within the amygdala result in profound changes in social interactions and emotional behavior in macaque monkeys. Further, we have discovered that the activation of the intermediate and deep layers of the superior colliculus (DLSC; a midbrain structure) by focal infusions of GABAA antagonist bicuculline, has a profound impact on emotional reactivity and defensive responses. In the proposed experiments, we will use the method of intracerebral focal drug infusions of either the GABA agonist muscimol or the GABA antagonist bicuculline aimed at various sites within either amygdala or DLSC to test further the role of these structures in socioemotional behavior. Specific Aim 1 will define specific nuclei within the amygdala responsible for GABA- mediated regulation of socioemotional responses. Aim 2 will test the hypothesis that disinhibition of DLSC will evoke aggressive behavior and emotional hyperactivity. Aim 3 will assess the role of DLSC and amygdala in fear-potentiated startle, a conditioning paradigm that is altered in human patients with PTSD. Social interactions will be assessed in dyads, each infused animal will be paired with a familiar non-infused partner; videotaped behaviors will be analyzed by two independent observers using a standardized behavioral categorization. Special attention will be paid to reciprocal social interactions, aggressive behavior, and emergence of any abnormal behaviors (e.g., stereotypies, self-directed behaviors). Emotional reactivity will be tested by presenting the animals with a standard set of stimuli (neutral, positive, and negative). An understanding of the functional relationship between the amygdala-derived and colliculus-derived regulation of social interactions and emotional tone is expected to reveal novel targets for both etiology and therapeutic intervention for affective and anxiety disorders.